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Co-based water-atomised powder composition for die compactionRelated Patent Categories: Powder Metallurgy Processes, Powder Metallurgy Processes With Heating Or Sintering, Metal And Nonmetal In Final Product, Nonmetal Is Elemental CarbonCo-based water-atomised powder composition for die compaction description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060198751, Co-based water-atomised powder composition for die compaction. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This is a Continuation of U.S. patent application Ser. No. 10/801,647, filed Mar. 17, 2004, and claims the benefit under 35 U.S.C. .sctn.119(a)-(d) of Swedish Patent Application No. 0300881-0, filed Mar. 27, 2003, and under 35 U.S.C. .sctn.119(e) of U.S. Provisional Patent Application No. 60/482,866, filed Jun. 27, 2003. FIELD OF THE INVENTION [0002] The present invention concerns powder metallurgy. More specifically the present invention concerns a cobalt-based powder metal composition and a method for producing components thereof, especially for heavy duty applications. BACKGROUND OF THE INVENTION [0003] Cobalt-based alloys, such as Stellite.RTM. (Trade Mark for Co--Cr--W alloys) are hard alloys that are extremely resistant to many forms of wear. Products of these alloys show high hardness over a wide temperature range and are resistant towards corrosion. These products are used for inter alia casting of various kinds of components such as machine parts (bearing shells, valve seat inserts etc) or other components where high density, high strength and wear resistance are required. [0004] Cast material often suffers from micro structural defects and carbide segregation. Carbide segregation leads to inhomogenously distributed hard phases. Disadvantages with such materials are lack of fracture toughness and poor machinability. [0005] Powder metallurgy (PM) products generally possess a more homogenous microstructure than cast products. Further advantages with the PM production method are that costly machining into final shape may be excluded or minimized in comparison with traditional casting methods and that the method is more suitable for producing large quantities of small articles. [0006] Attempts have been made over the years to produce cobalt-based products using the PM technology. Thus U.S. Pat. No. 4,129,444 discloses a process wherein atomised Co-based alloy powders are coated with a binder and then consolidated to produce discrete bodies that are dried, crushed and screened to obtain agglomerates. The agglomerates are pressed into green compacts which are sintered at high temperature. Furthermore U.S. Pat. No. 5,462,575 discloses a powder metallurgy component prepared of a gas atomised Co--Cr--Mo alloy powder. The alloy powder is filled in a canister and baked in vacuum to degas the powder and the powder filled canister is thereafter consolidated, preferably by hot isostatic pressing (HIP). OBJECTS OF THE INVENTION [0007] An object of the invention is to provide a new Co-based powder metal composition which can be used in conventional PM processes. [0008] Another object is to provide a Co-based powder metal composition with high compactibility which can be compacted to high green density and high green strength. [0009] Still another object is to provide a green body of a cobalt based alloy which can be machined before sintering. [0010] A further object is to provide a powder metal composition which can be compacted and sintered to high density without high sintering temperatures. SUMMARY OF THE INVENTION [0011] These objects as well as other objects that will be apparent from the description below, have now been obtained according to the present invention by providing a new Co-based powder metal composition. Critical features of this composition are that the composition comprises a Co-based pre-alloyed powder with irregularly shaped particles admixed with graphite. Furthermore the Co-based pre-alloyed powder should include less than 0.3% by weight of carbon and at least 15% by weight Cr. The Co-based pre-alloyed powder preferably comprises at least 30% by weight and preferably less than 80% by weight Co. [0012] The invention also concerns a method comprising the steps of providing a powder metal composition according to the invention and compacting the composition in a die at a pressure of at least 400 MPa to a component of desired shape. DETAILED DESCRIPTION OF THE INVENTION [0013] The Co-based pre-alloyed powder in the composition according to the invention may be produced by subjecting a melt having the desired composition to atomising by water. [0014] The Co-based pre-alloyed powder according to the invention comprises less than 0.3% by weight carbon. The carbon content of the powder is however preferably less than 0.1% by weight, and most preferably less than 0.05% by weight (i.e. essentially free from C except for inevitable impurities). [0015] The Co-based pre-alloyed powder comprises at least 15% by weight and preferably less than 35% by weight Cr. [0016] The addition of Cr improves the strength of the Cobalt matrix by solution hardening and/or carbide formation. These effects are further improved by the addition of W and/or Mo. [0017] Other elements which may be included in the Co-based pre-alloyed powder may be chosen from Ni, Fe, Si, Mn, V and B. [0018] A preferred pre-alloyed powder according to the invention comprises 15-35% by weight Cr, 0-20% by weight W, 0-25% by weight Ni, 0-5% by weight Si, 0-5% by weight Fe, 0-10% by weight Mo, balance Co and less than 0.3% by weight C. [0019] Another preferred powder according to the invention further comprise 0-3% by weight Mn, 0-4% by weight V and 0-4% by weight B. Continue reading about Co-based water-atomised powder composition for die compaction... 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